As Frank Ettin wrote above: Heller/ In the ruling, Justice Scalia wrote in the majority decision:

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Held:
Held:
1. The Second Amendment protects an individual right to possess a firearm unconnected with service in a militia, and to use that arm for traditionally lawful purposes, such as self-defense within the home.Pp. 2–53.
(a) The Amendment’s prefatory clause announces a purpose, but does not limit or expand the scope of the second part, the operative clause. The operative clause’s text and history demonstrate that it connotes an individual right to keep and bear arms. Pp. 2–22.
(b) The prefatory clause comports with the Court’s interpretation of the operative clause. The “militia” comprised all males physically capable of acting in concert for the common defense. The Antifederalists feared that the Federal Government would disarm the people in order to disable this citizens’ militia, enabling a politicized standing army or a select militia to rule. The response was to deny Congress power to abridge the ancient right of individuals to keep and bear arms, so that the ideal of a citizens’ militia would be preserved. Pp. 22–28.
(c) The Court’s interpretation is confirmed by analogous arms bearing
rights in state constitutions that preceded and immediately followed the Second Amendment. Pp. 28–30.
(d) The Second Amendment’s drafting history, while of dubious interpretive worth, reveals three state Second Amendment proposals that unequivocally referred to an individual right to bear arms. Pp. 30–32.

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1. Operative Clause.
a.
“Right of the People.” The first salient feature of the operative clause is that it codifies a “right of the people.” The unamended Constitution and the Bill of Rights use the phrase “right of the people” two other times, in the First Amendment’s Assembly-and-Petition Clause and in the Fourth Amendment’s Search-and-Seizure Clause. The Ninth Amendment uses very similar terminology (“The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people”). All three of these instances unambiguously refer to individual rights, not “collective” rights, or rights that may be exercised only through participation in some corporate body.5

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What is more, in all six other provisions of the Constitution that mention “the people,” the term unambiguously refers to all members of the political community, not an unspecified subset.

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This contrasts markedly with the phrase “the militia” in the prefatory clause. As we will describe below, the “militia” in colonial America consisted of a subset of “the people”—those who were male, able bodied, and within a certain age range. Reading the Second Amendment as protecting only the right to “keep and bear Arms” in an organized militia therefore fits poorly with the operative clause’s description of the holder of that right as “the people.”We start therefore with a strong presumption that the Second Amendment right is exercised individually and belongs to all Americans.

That should give you a start. Here's a link to the full decision. It makes a good read, and a good reference.